This invention relates to the use of a digital processor or computer for compensation of sensors.
A wide variety of sensors are utilized for different purposes including the control of processes and equipment. When utilizing sensors for control purposes, it is particularly important, in many instances, to avoid gain, offset, drift and degradation problems which can produce unreliability.
In the area of optical sensors, an LED (light emitting diode)/phototransistor combination is widely used in a variety of applications. One distinct advantage of this combination is the relatively low cost. However, the gain and offset of the combination differ from one LED/phototransistor to another LED/phototransistor, and the LED and phototransistor are subject to short term drift with temperature as well as long term degradation. Although such a combination may be utilized in certain digital applications, the combination is generally unsuitable for analog applications. Some of the foregoing difficulties may be eliminated by AC coupling the LED to the phototransistor. However, variations in gain still present a problem. Moreover, the AC coupled combination results in a relatively high cost. Another optical combination which is sometimes utilized comprises a sensor, a reference, a comparator and a uniform light source. A photocell may be utilized in conjunction with the uniform light source as the reference and the sensor itself may comprise a phototransistor. Although gain, offset, short and long term drift are minimized, such a combination is quite costly and therefore unsuitable for many applications.